1. Field of the Invention
The present invention relates to a receiving apparatus and a communication system for receiving a serial signal and decoding the received serial signal into an information signal including information data. More specifically, the present invention relates to a receiving apparatus and a communication system capable of decoding a received serial signal into an information signal including information data even if noise is included in the received serial signal.
2. Description of the Related Art
In a serial data transmission method in which a plurality of information bits are transmitted serially, the following so-called start stop synchronization method is used. In this method, transmission is made asynchronously so that a start bit and a stop bit are added respectively before and after data for identification of the beginning and the end of a frame, and then, the start bit is detected at a receiving station for frame synchronization.
According to the above-mentioned prior art serial data transmission method, if a noise signal (pulse) is included before the start bit, it is such a possibility that the noise signal (pulse) may be detected as the start bit. Further, if the noise signal (pulse) is included within the data, it is such a possibility that the noise signal (pulse) may be detected as valid data.
Attempts have been made in order to avoid the above-mentioned problems, and the following method. for receiving serial data is disclosed in Japanese Patent Laid-Open Publication No. 6-152576. If noise is expected in a received signal, a signal having a pulse width not greater than a predetermined pulse width are eliminated as a noise signal from the received signal so that the noise will not cause any detection error, thus a noise signal is eliminated from the received signal, and frame-synchronized data is obtained based on the noise-eliminated signal.
In addition, a method for correcting a bit drop or the like from a run-in signal is disclosed in Japanese Patent Laid-Open Publication No. 58-42336.
The above-mentioned prior art receiving apparatus has the following problems. With the arrangements described above, the prior art receiving apparatus cannot remove a noise signal (pulse) if the noise signal (pulse) has a width similar to that of the valid signal. Therefore, if a noise signal (pulse) having a pulse width similar to that of the synchronizing signal exists near the synchronizing signal, the noise signal (pulse) may be detected as a start pulse. Further, if a noise signal (pulse) having a pulse width similar to that of the data signal exists in the data, the noise pulse may be detected as a valid data signal.
In order to prevent such an error detection, there is such an idea of increasing the pulse width of the synchronizing signal or the data signal. In this case, the increased pulse width of the synchronizing signal or of the data signal decreases transmission speed or the amount of data transmittable within a given time interval.